The present invention relates to polyesters based on dicarboxylic or polycarboxylic acids and diols or polyols, the polyesters comprising at least one unsaturated dicarboxylic or polycarboxylic acid and at least one alkoxylated diol or polyol, to processes for preparing them and to their use.
Unsaturated amorphous polyester resins (UP resins) are prepared by condensing saturated and unsaturated dicarboxylic acids or their anhydrides with diols. Their properties are dependent largely on the nature and proportion of the starting materials. The use of such unsaturated amorphous polyester resins for promoting adhesion is conventionally known as described in DE 2409800, EP 114208 and EP 934988. In the polyester resin it is generally carboxyl groups which mediate adhesion to the substrate, while remaining hydroxyl groups, for example, in two-component systems, or polymerizable double bonds in oxidatively drying or radiation-curing systems, are incorporated by reaction.
Used frequently as carriers of the polymerizable double bonds are α,β-unsaturated acids, primarily maleic acid or its anhydride, or fumaric acid. Besides fumaric and maleic acid and the anhydride of the latter, examples of other polymerizable acids include citraconic, itaconic and/or mesaconic acid. Unsaturated diols are of minor importance. The reactivity of a polyester resin increases in line with the amount of double bonds therein, and in the event of high crosslinking, results in a relatively brittle end product. The desired brittleness is therefore adjusted by co-condensation with saturated aliphatic or aromatic dicarboxylic acids.
The individual grades of UP resin differ not only in the components used for their preparation, but also in the proportion of saturated to unsaturated acids, which determines the crosslinking density on polymerization; the degree of condensation, i.e. the molar mass; the acid number and OH number, i.e. the nature of the end groups in the chain molecules; the monomer content; and also the nature of the additives (Ullmann's Encyclopaedia of Industrial Chemistry, vol. A21, p. 217ff., 1992).
Also known, is the additional use of aromatic and/or aliphatic and/or cycloaliphatic monocarboxylic acids and/or dicarboxylic acids and/or polycarboxylic acids, such as, for example, phthalic acid, isophthalic acid, terephthalic acid, 1,4-cyclohexanedicarboxylic acid, succinic acid, sebacic acid, methyltetra- and methylhexahydrophthalic acid, hexahydrophthalic acid, tetrahydrophthalic acid, dodecanedioic acid, adipic acid, azelaic acid, isononanoic acid, 2-ethylhexanoic acid, pyromellitic acid and/or trimellitic acid.
Diol components used include linear and/or branched, aliphatic and/or cycloaliphatic and/or aromatic diols and/or polyols. Examples thereof are ethylene glycol, 1,2- and/or 1,3-propanediol, diethylene, dipropylene, triethylene and tetraethylene glycol, 1,2- and/or 1,4-butanediol, 1,3-butylethylpropanediol, 1,3-methylpropanediol, 1,5-pentanediol, cyclohexanedimethanol, glycerol, hexanediol, neopentyl glycol, trimethylolethane, trimethylolpropane and/or pentaerythritol and also bisphenol A, B, C, F, norbornylene glycol, 1,4-benzyldimethanol and -ethanol, 2,4-dimethyl-2-ethylhexane-1,3-diol.
In particular the use of Dicidol (tricyclodecanedimethanol, octahydro-4,7-methano-1H-indenedimethanol) as a diol component for the preparation of unsaturated polyester resins has been described in DE 953117, DE 2245110, DE 2721989, EP 114208 and EP 934988. Tricyclodecanedimethanol consists primarily of the isomeric compounds 3,8-bis(hydroxy-methyl)tricyclo[5.2.1.02,6]decane, 4,8-bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane and 5,8-bis(hydroxymethyl)tricyclo[5.2.1.02,6]decane. The effect of adding Dicidol is to improve the tack-free state not only of the pure polyester resin but also later in the dried film, and to positively influence the storage stability of the resin. The through-drying of the coating is improved as well through the use of Dicidol.
Particularly in the case where Dicidol is used, however, the conventional polyester resins are solid resins. The metering of solids is often difficult, however, especially in the case of small and medium companies producing coating materials. The addition of solids has to be made by tipping sacks, in a physically demanding and inconvenient operation. Apart from the occupational physiology disadvantage, the resultant dusts also harbour safety problems, since solids can in principle lead to instances of dust explosion.
Solid resins can in principle also be metered in the form of a solution in organic solvents. Metering in dissolved form, however, adds the disadvantage that the user, to start with, has to accept the solvent mandated by the manufacturer. Moreover, the formulation especially of modern high-solids coatings, with a frequent necessity for a solvent fraction of up to 50 wt % in order to achieve a processable solution viscosity of the solid resin, is impossible.
DE 2402841 describes low-viscosity polyesters with low solvent content and also their reaction with amino resins to form impact-resistant coatings. Analogous teaching is contained in DE 2454025. The polyesters disclosed in both of these documents are based on bisphenol A.
It was an object of the present invention, therefore, to find an adhesion-promoting additive which improves properties of coating materials, such as the adhesion or the non-volatile fraction, for example, but with which at the same time it is possible to avoid the addition of further solvents. The adhesion-promoting additive ought, furthermore, to have a general activity in all binder systems.